Stihl 108 User Guide

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Circularsawblade 200
(chisel andscratcher tooth)
Fitthe appropriate stop
before mounting circularsawblade.
Fitting thestop seechapter Mounting
the Deflector.
30
Mounting circularsawblade
•Layyour brushcutter onitsback
with thegear head facing up.
• Position sawblade
(3)on
the thrust plate(4)-
teeth mustpointinclockwise
direction.
• Slipthethrust washer
(5)
andrider plate(6)over
the drive shaft
(7).
•Block thedrive shaft.
• Screw mounting nut
(8)counterclockwise onto
drive shaftandtighten down
securely.
Releasing mountingnut
•Block thedrive shaftand
unscrew themounting nut
clockwise.
Ifthe mounting nutbecomes slackdue
to frequent loosening andretightening, fit
a new one. 
						

							Fuel
Yourtwo-strokeenginerequires a
mixture ofbrand-name gasolineand
quality two-stroke engineoilwith the
classificationTe.
Useregular branded unleaded gasoline
with aminimum octanenumber of
90 ROZ (U.S.A./Canada: pumpoctane
min. 89!).
Iftheoctane number ofthe
regular gradegasoline
inyourarea is
lower
us5=lpremium unleaded fuel.
Fuel withalower octane number may
result
inpreignition (causingpinging)
which
isaccompanied byan increasein
engine temperature. This,inturn,
increases therisk ofthe piston seizure
and damage tothe engine.
The chemical composition ofthe fuel
is
also important. Somefueladditives not
only detrimentally affectelastomers
(carburetor diaphragms, oilseals, fuel
lines etc.), butmagnesium castingsas
well. This could cause running problems
or even damage theengine. Forthis
reason
itisessential thatyou useonly
name branded fuels!
Use only STIHL two-stroke engineoilor
equivalent brandedtwo-stroke air-cooled
engine oilswith theclassification TCfor
mixing.
We recommend STIHL
50:1two-stroke
engine oilsince itis specially formulated
for use
inSTIHlengines. Themixratio
with
STIHloilis50:1(50 parts gasoline
to 1part oil),or
25:1(25parts gasoline to
1 part oil)with other branded two-stroke­
air-cooled engineoils. Do
not use BIAor
TCW(two-stroke
water cooled) mixoils!
Take carewhen handling gasoline.
Avoid directcontact withtheskin and
avoid inhaling fuelvapour.
The canister shouldbekept tightly
closed
inorder toavoid anymoisture
getting intothemixture.
The fueltank andthecanister
inwhich
fuel mixisstored should becleaned
from timetotime.
Fuel mixages:
Only mixsufficient fuelforafew days
work, nottoexceed 30days ofstorage.
Store
inapproved safetyfuel-canisters
only. When mixing, pouroilinto the
canister first,andthen addgasoline. Gaso-
STIHL Otherbranded
line engineoil
TCoils
50:125:1
Liters Liters(cc)
Liters (cc)
1 0.02 (20)0.04 (40)
5 0.10(100) 0.2(200)
10 0.20(200)
OA(400)
15
,:-0.30(300) 0.6(600)
20
OAO(400) 0.8(800)
25 0.50(500) 1.0
(1000)
Gaso- STIHL Otherbranded
line engineoil TCoils
50:125:1
US gal. US
fl.oz USfl.oz
1 2.6
5.1
21/26A12.8
5 12.8
25.6
31 
						

							FuelingFittingtheHarness
Beforefueling, cleanthefiller capand
the area around it
toensurethatnodirt
falls intothetank.
Always thoroughly shakethemixture in
the canister beforefueling yourmachi­
ne. Change
thefuel pick upbody every year.
Before storing yourmachine foralong
period, drainandclean thefuel tank and
run engine untilcarburetor is
dry.
Modelswithaloop handle comewithout
a harness (available asspecial acces­
sory forthese models).
Shoulder strap
Useofthe carrying strapisdescribed
in chapters SafetyPrecautions and
Selecting theCutting Tool.
Warning!Inordertoreduce therisk of
bums orother personal injuryfromesca­
ping gasvapor andfumes, remove the
fuel filler capcarefully soastoallow any
pressure build-up
inthetanktorelease
slowly.
WarningAfter fueling, tightenfuelcap
assecurely aspossiblebyhand.
32
•....,.Put onthe shoulder strap(1).
Adjust lengthuntilthespring
hook (3)rests against yourrighthip. 
						

							Fullharness
• Putonthe fullharness (2).
• Adjust lengthuntilthespring
hook (3)rests against yourrighthip.
Use ofthe carrying strapisdescribed
inchapters SafetyPrecautions and
Selecting theCutting Tool. Balancing
thebrushcutter
• Attach thespring hook
(3)totheclamp(4)onthe drive shaft­
slacken thescrew (5).
• Slide theclamp upordown
the drive shaft.
•
Tightenthe screw moderately. •
Letgoofthe brush cutter andcheck
toseehowitisbalanced:
mowing heads,FixedLineHead
and
brush knifemust restlightly
onthe
ground. Circular sawblades muststay
abottt30cm/1ft(A)clear ofthe
ground.
•
Tightenthe screw firmly.
33 
						

							Starting
1
•Observe safetyprecautions -see
section SafetyPrecautionsinthis
manual.
• Hold down thethrottle trigger
interlock (1)and squeeze
the throttle trigger(2).
• Move theslide control (3)
toSTART position.
• Now release thethrottle trigger, slide
control andtrigger interlock
inthatorder=Thisisthe
starting-throttle position.
34
Ifengineiscold:
Setthechoke lever(4)to.L
Ifengineiswarm:
Set thechoke lever(4)to...
Also usethissetting ilengine hasbeen
running but
isstillcold. •
Puttheunit onthe ground:
Itmust restsecurely onthe engine
support anddeflector. Checkthat
the cutting tool
isnottouching the
ground orany other obstacles.
• Make sureyouhave afirm
looting: Holdtheunit with youleft
hand andpress itdown
firmly ­
yourthumb shouldbeunderthe
housing.
• Donot stand orkneel
onthe drive
shaft! 
						

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2
•Pullthestarter gripslowly withyour
right hand untilyoufeel
itengage ­
and then give
itabrisk strong pull.
Do not pull outstarter ropemore
than 70cm (27)-
itmight break.
Do not letthe starter gripsnap
back -guide
itslowly intothe
housing sothat thestarter rope
can rewind properly. When
engine beginstofire:
Ifengine iscold:
Set choke lever(4)
to-
andcontinue cranking untilengine runs.
Ifengineiswarm:
Continue crankinguntilengine
runs_
Assoon aswarm engine runs:
• Blipthethrottle trigger(2)-
the slide control (3)moves tothe
runpositionI,and theengine
returns
toidling speed.
•
Make~urecarburetor iscorrectly
adj,usted-cutting toolmust not
rotate whenengine
isidling.
Your brushcutter
isready for
operation.
35 
						

							Toshutdown engine:
• Move slidecontrol (3)
toSTOP.
At very lowoutside temperatures:
Allow engine towarm up
As soon asengine runs:
• Blipthethrottle trigger-
the slide control
(3)moves tothe
run position
I,and theengine
returns toidling speed.
• Open throttle slightly -
warm upengine forshort period.
36
Ifthe engine doesnt start:
Ifyoudidnot move thechoke
lever
to.L
quickly enough aftertheengine
began tofire, thecombustion chamber
is flooded.
Remove sparkplugterminal
(5)-
• Unscrew anddryoffthe
spark plug.
• Setslide control
toSTOP.
• Open thethrottle fully.
• Pullthestarter ropeseveral timesto
clear thecombustion chamber. •
Refit thespark plugandconnect
the spark plugterminal.
• Setslide control toSTART.
• Setchoke lever
to...
even ifengineiscold.
•
Nowstart theengine.
Fuel tank rununtil dryand then
refueled
• Continue cranking-
Engine willnot start immediately
because fuelpump hastobe pri­
med withfuel. 
						

							AdjustingCarburetor
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Thecarburetor hasbeen adjusted for
optimum performance underthe
barometric pressureandclimatic
conditions atthe factory.
Basic setting
Thissettingisthestarting pointforfine
tuning andcanbeused asthe
standard setting.
•Check airfilter andclean it if
necessary.
• Carefully screwthehigh speed
adjusting screw(H) and lowspeed
adjusting screw(L)down ontotheir
seats (clockwise) andmake the
following adjustments: H
Open 1full turn
L Open 1full tum
• Start theengine andadjust idling
speed withtheidle speed adjusting
screw
LAor LD:
cutting toolmust notrotate.
This standard setting
istheoptimum
setting
ofthe high speed adjusting screw
for normal operation atan altitude of
about 300m/1000
Itabove sealevel.
Itensures yourmachine willdeliver
maximum power,befuel efficient and
operate reliably.
Itmaybenecessary fine-tunethe
carburetor
ifoperatingconditionschange,
e.g. higher orlower altitudes, extreme
changes
inhumidity andtemperature or
ifyoufitadifferent cuttingtool:
Thefinetuning procedures described
below ensure maximum performance
under
t~enewoperating conditions.
37 
						

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Finetuning
•Mount thecutting tool.
Machines withcutting head:
•Trim linetocorrect length:
Lines mustextend asfar asline
limiting bladeonthe deflector
• Carry outthebasic setting.
• Warm upengine byrunning
itfor
about 1minute atfull throttle and
then return
toidlespeed.
• Back offhigh speed adjusting screw
(H)onehalfturn (counterclockwise).
• Runengine atfull throttle androtate
high speed adjusting screw
(H)
carefullyclockwise untilyouhear
38
nofurther increaseinRPM­
back offscrew oneeighth turn.
Machines withmetal cutting tool:
Atachometer isnecessary forthe
following adjustment.
Ifnotachometerisavailable,.....,.
do not turn screws beyond thebasic
setting.
• Carry outthebasic setting.
• Warm upengine byrunning
itfor
about 1minute atfull throttle and
then return toidle speed. •
Back offhigh speed adjusting screw
(H)onehalfturn (counterclockwise).
• Runengine atfull throttle and
rotate highspeed adjusting screw
(H)carefullyclockwise until
maximum permissible speedof
12,000 RPM
isreached.
Turning thescrew
(H)any further
in the clockwise directionwill
make thefuel-air mixture too
lean -
thiscould damage theengine! 
						

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Adjustingidlespeed
Itisusually necessary tochange
the setting ofthe idle speed
adjusting screw
(LAorLD)after every
correction
tothe low speed
adjusting screw
(L).
Engine stopswhileidling
Turntheidle speed
adjusting screw
(LAorLD)
clockwise untilengine runs
smoothly -cutting
tool must notrotate.
Cutting toolrotates when
engine isidling
Turn theidle speed adjusting
screw
(LA orLD)counterclockwise
until cutting toolstops rotating ­
then back offscrew about
another onehalftum from that
position.
Erratic idlingbehavior,
poor acceleration
Idlesetting istoo lean.
Turn thelow speed adjusting
screw
(L)counterclockwise until
engine runsandaccelerates
smoothly.
Exhaust smokesatidle speed
Idlesetting istoo rich.
Turn thelow speed adjusting
screw
(L)clockwise until
engine speeddrops. Thenturn
screw backonequarter turn
and
ch~kthat engine still
accelerates smoothlywhen
you open thethrottle.
39